[docs] Fix formatting in clients/superset.rst

[steveburnett]

Description

Fix formatting in clients/superset.rst, and simplify steps.

Motivation and Context

Standardized formatting for UI items, simplified steps for reader benefit. Builds on the work in #23194.

Impact

Documentation.

Test Plan

Local instance of Superset and a local instance of Presto server to test and simplify steps.
Local doc builds of revised documentation and review of built docs.
CI.

Contributor checklist

• Please make sure your submission complies with our development, formatting, commit message, and attribution guidelines.
• PR description addresses the issue accurately and concisely. If the change is non-trivial, a GitHub Issue is referenced.
• Documented new properties (with its default value), SQL syntax, functions, or other functionality.
• If release notes are required, they follow the release notes guidelines.
• Adequate tests were added if applicable.
• CI passed.

Release Notes

== NO RELEASE NOTE ==